This invention relates to a device for measuring components of force and moment applied to a vehicle wheel shaft from a rotating tire and, more particularly, to a device for processing force and moment indicative signals supplied from a load cell structure rotating with the tire to obtain corresponding components about a predetermined co-ordinate fixed to the vehicle.
An example of a load cell structure used for this purpose is disclosed in U.S. Pat. No. 4,448,083. This prior art structure comprises a central hub portion, a circumferential rim portion and flexures formed between these portions to which are attached a plurality of strain sensing elements. The load cell structure is designed to be coupled to a vehicle to be tested by fixing the rim portion to the vehicle body and pivoting the hub portion through a bearing on a wheel shaft mounted with a tire. Therefore, it is rather easy to obtain the component forces and moments about a co-ordinate fixed to the vehicle by simply combining electric signals provided by the strain sensing elements as set forth in the above-cited U.S. patent. However, in order to mount a load cell structure of this type on a conventional automobile, it is necessary to prepare its mounting space by removing the brake drum, which may result not only in substantial danger in a high speed driving test, but also in significant difficulty in a steering or turning test.
Japanese patent opening gazette No. 60-38632 has proposed a load cell structure designed to be fixed to a wheel shaft to rotate with a tire. This structure also includes a central hub portion, a circumferential rim portion and strain sensing flexures formed between these portions, as in the prior art structure. In contrast, however, the hub portion is fixed directly to the wheel shaft and a tire is coupled to the rim portion through a modified tire rim as described later. With this type of load cell structure, therefore, it is unnecessary to remove the brake drum or to modify the vehicle in any way other than by using the modified tire rim. Consequently, it becomes possible to mount all wheel shafts with load cell structures and drive the vehicle freely and safely at a desired speed. In order to obtain the desired component forces and moments about a specific co-ordinate fixed to the vehicle as in the prior art device, the electric signals from the strain sensing elements, which may be derived, for example, through slip rings, must be suitably processed by arithmetic means. Such means is not disclosed in the above-cited reference.